The invention relates to a process for producing a water-soluble package. In particular the invention relates to a process for producing a thermoformed water-soluble package.
Water-soluble packages are known in the detergent and agrochemical industries and generally comprise either vertical form-fill-seal (VFFS) envelopes or thermoformed envelopes. In one of the VFFS processes, a roll of water soluble film is sealed along its edges to form a tube, which tube is the heat sealed intermittently along its length to form individual envelopes which are filled with product and heat sealed. The thermoforming process generally involves moulding a first sheet of water soluble film to form one or more recesses adapted to retain a composition, such as for example a solid agrochemical composition, placing the composition in the at least one recess, placing a second sheet of water soluble material over the first so as to cover the or each recess, and heat sealing the first and second sheets together at least around the recesses so as to form one or more water soluble packages.
Generally, water-soluble packages suffer a number of disadvantages. First, as the packages are susceptible to moisture, the composition, which can be contained within the package, is limited. Secondly, the storage and transport of such packages must be carefully controlled as humidity in the atmosphere can weaken the structural integrity of the formed packages.
It is an object of the present invention to overcome at least some of the above disadvantages.
According to the invention there is provided a process for forming a water soluble package, the process being characterised in that the formed packages are conditioned in an atmosphere of raised Relative Humidity (RH) for a period of time. In the process of the invention, the package may be formed by any convenient method such as VFFS, thermoforming, HFFS and the like. In one process according to the invention the packages are conditioned, ideally after sealing, in an environment having a RH greater that 50% at ambient temperature, preferably between 60 and 80% RH, ideally between 65 and 70% RH. Typically, the temperature of the conditioning environment will be in the region of 15 to 25 degrees C, ideally about 20 degrees C. In one process according to the invention, the packages are conditioned for a time sufficient at least partially to plasticise the water soluble films of the packages, thereby rendering the packages less brittle and more impact resistance. The time required will vary according to the RH and the temperature but will typically be between about 1 and about 10 minutes.
The process includes a step of packaging the conditioned packages within a secondary pack. In this regard the secondary pack should include at least a partial moisture barrier such as polypropylene, polyester, aluminium foil, PVDC, waxed cardboard and the like. Typically the MVTR of the material of the secondary packs is in the region of 1 to 20 g/m2/24 hours. In one preferred process of the invention, the conditioned packages are packed into the secondary pack in the conditioning environment, that is to say, the packages are packed into the secondary pack in an atmosphere of raised relative humidity. The choice of the secondary pack may be chosen from materials which are well known to a person skilled in the packaging field, given the requirement of preventing or inhibiting moisture transmission. Examples of suitable packaging would be wax or polyethylene lined cardboard boxes. It has been found that when water-soluble packages are suitably conditioned, the water-soluble films have a greater impact resistance, and hence will be more sturdy and resilient in transport.
In one preferred process of the invention, at least some of the initial steps of the process leading up to the sealing of the package are carried out in an atmosphere having a RH lower than that of the conditioning atmosphere. Suitably this preconditioning of the packages may be carried out in an atmosphere having a RH less than 50%, typically approximately 40% RH. Ideally this preconditioning is carried out during the forming, filling and sealing steps. It has been found that such pre-conditioning of the film during the forming, filling and sealing stages effectively stiffens up the film and allows for easier handling and processing.
When the process of the invention involves thermoforming the packages, the recess or recesses formed in the first film of water-soluble material may be retained in a formed shape by means of the application of a vacuum. In this regard the recess or recesses may be formed in the first sheet by heating the film over a die having one or more cavities, wherein once heated the film falls into the cavities and assumes the shape of the cavity. The cavities thus may include means for pulling a vacuum on the formed film. The vacuum in this instance may be maintained throughout the subsequent filling and sealing steps. Where the die includes a number of cavities, the process will include the additional steps of cutting the formed packages and ejecting the cut individual packages from the die.
In a preferred embodiment of the invention the film is a polyvinyl alcohol, or modified polyvinyl alcohol, film. Typically, the composition is a fluent composition such as for example a liquid, gel or paste. When the composition is a liquid, ideally the liquid will have a viscosity of up to 1000 centipoise, when measured at at a shear rate of 105/second at 20 degrees C. Preferably, each package will contain up to one litre of composition, ideally between 10 and 50 mls, most preferably between 15 and 30 mls. In an envisaged embodiment, the composition will include detergent suitable for use in the machine washing of laundry or dishes.
The invention also relates to water-soluble packages obtainable by the process of the invention, and the use of such packages in the machine washing of laundry and dishes.